Capacity sensitive relays



April 19, 1960 F. L. MALTBY ET AL CAPACITY SENSITIVE RELAYS Filed Feb. 7, 1956 7m ATT OM CAPACITY SENSITIVE RELAYS Frederick L. Maltby, Riverton, NJ., Edward Cozzette, Huntington Station, N.Y., and Joseph W. Philippi, Woodbury, N.J., assiguors to Robertshaw-Fulton Controls Company, Richmond, Va., a corporation of Delaware Application February 7, 1956, Serial No. 563,921

4 Claims. (Cl. 317-142) This invention relates to capacity sensitive relays and safe controlled relays employing a time delay mechanism.

It is an object of this invention to utilize a time delay mechanism in cooperation with a capacity relay for delaying the time of energization of the relay.

With these and other objects in view, the invention may take the form of an oscillator circuit including an oscillatory tank circuit inductively coupled to a charging circuit for delaying the energization of an electronic relay circuit. The relay circuit serves to actuate a pump switch and an indicator light depending upon the normal operation of the device. A capacity sensitive probe is connected to the oscillatory tank circuit and is utilized to pick up the stray capacitance which varies according to the level of the fluid in a container thereby varying the feedback generated in the tank circuit.

The R.F. generated in the tank circuit is utilized to control the grid voltage of a vacuum tube having a relay in the anode circuit thereof. However, this R.F. voltage is diverted by a capacitor located in the grid circuit and which is adapted to be charged before the grid current attains sufficient value for permitting the increase of current in the anode circuit. Consequently, the time at which the relay would normally be energized is delayed until the capacitor is fully charged. When the R.F. voltage no longer is generated, the capacitor discharges the charged induced therein into the grid circuit for delaying the deenergization of the relay. As a result of the time delay circuit the level of the material may slightly overshoot or undershoot the desired level thereby increasing the range of levels at which the relay will become operative. In this manner, the periods of operation for the relay and the. energization of the oscillator circuit and the time delay tube are greatly diminished thus lengthening the operating life of the components. e

Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawing wherein:

Fig. l is a diagrammatic view showing an application of a low level fail-safe capacity sensitive relay embodying the essentials of the present invention; and

Fig. 2 is similar to Fig. 1 but showing a high level fail-safe capacity relay.

Referring more particularly to Fig. '1, the system embodying this invention is shown as comprising an oscillator circuit It), a probe 12 for picking up stray capacitance for the oscillator circuit 10, a time delay circuit 14 for controlling the operation of a relay 16 and a valve 118 operable in response to the energization of the relay 16.

The oscillator circuit 18 comprises an electron discharge tube 20 having an anode 22, a cathode 24 and a grid 26. Coupled to the electron discharge tube 20 is an oscillatory tank circuit comprising a coil 28 and a carpacitor 36 connected therewith, one end of the coil 28 being grounded at 32. Completing the tank circuit is a capacitor 34 connected to one end of the coil 28 and Unitfid ltes Paten more particularly to capacity type high and low level fail- ICC Patented Apr. 19, 1960 to the capacitor 30, and a connection between the cathode 24 of the tube 20 and a tap 29 in the coil 28. The anode 22 of the tube 20 is coupled to one end of the tank circuit through a blocking capacitor 38 while interposed between the grid 26 and the capacitor 30 is a grid leak resistor 40. I A

Power. is supplied to the oscillator circuit 10 by a transformer 42 having a primary winding which is connected across a source L1, L2 of alternating current supply and a secondaryv winding 44 having a terminal 46 grounded at 48. Another terminal 50 of the secondary winding 44- is coupled to the oscillator circuit 10 by a conductor 52 connected to the anode 22 through a suitable resistor 54 and a small R.F. choke 56 in series with anode 22.

As shown in the drawing, the tank coil 28 is inductively coupled to a coil 60 of the time delay circuit 14 and thus provision is made for inducing thecircuit 14 with the R.F. voltage generated in the oscillator circuit 10. One terminal of the coil 60 is grounded at 62 through a conductor 64 and the other terminal of the coil 6% is connected to a diode 66 preferably 1N54A germanium diode, through a resistor 68. The output of the diode 66 serves to charge a capacitor 70 which is grounded at 62 and to apply a positive voltage upon a grid 72 of an electron discharge tube 74 having an anode 76 and a cathode 78. A variable resistor 79 and a fixed resistor 80 are connected in series across the charging capacitor 70 for a purpose tobe described hereinafter, and an R.F bypass capacitor 82 is connected between the grid 72 and the ground 62.

Power is supplied to the time delay circuit 14 by the transformer 42 through the conductor 52 connected to the anode 76 and a conductor 84 connected between the cathode '78 and a terminal 86 of a secondary winding 88 of the transformer 42. The winding 88 has its other end connected to the ground 48 and, together with a resistor 99 in serie's therewith and the cathode 78, serves to deliver a current limiting bias on the cathode 78.

An excitor coil 92 of a relay 94 is connected in the anode circuit of the tube 74 to be energized thereby when the same is conducting. The relay 94 includes a movable contact arm 96 which is adapted to engage a fixed contact 98 when the coil 92 is energized. A coil spring 1% is held in tension between a rigid support 102 and the movable contact arm 96 to bias the same away from the fixed contact 98 when the coil 92 is deener gized. Mechanically coupled to the movable contact 96 is a second movable contact 104 which is adapted to engage a fixed contact 106 of an indicating system including a low level lamp 108. A suitable conductor 110 connects themovable contact 104 to the ground 48 and another conductor 1'12 connects the fixed contact. 106 to the lamp 108. It will be apparent that the lamp 108 will be energized when the relay 94 is deenergized and serves to indicate that a low level condition exists in the event of power failure in the electronic circuit.

The control apparatus of this invention may be of the usual industrial type comprising an open container 114 and a discharge pipe 116 connected thereto for conveying a material A, the level of which is to be controlled, out of the container 114. The electrically operable valve 118 may be of any well-known type having a conductor 119 connected to the supply line L2 and another conductor 120 connected to the fixed contact 98 of the relay circuit 16. To complete the relay valve circuit, a conductor 122 connects the movable contact 96 to the supply line L1. 7

The probe 12 constitutes the sensing mechanism of the present invention and may be located at a point near the top section of the container 114. The probe 12 includes an electrode 124 secured to the container 114 by a suitable insulating mounting means 126. The electrode 124 Operation Assuming that the fluid level of the material A surrounds the electrode 124, the capacitor 34 is adjusted to the value that will cause the oscillator circuit to oscillate, which will occur when the value of the capacitance 34 is such that impedance ratio of the capacitor 34 and the probe 12 is less than the impedance ratio of the two halves of the inductance coil 28. Oscillation in the circuit 10 generates an R.F. current in the coil 28 and since the coil 60 is coupled to the coil 28, the R.F. signal will be induced in the coil 60. This R.F. signal serves to charge the capacitor 70 and to apply a positive voltage on the grid 72 of the tube 74 that is sufiicient to overcome the current limiting bias fed to the cathode 78 by the winding 88 and the resistor 90. Since some of the R.F. current is being diverted to charging the capacitor 70, the time at which the grid 72 would normally acquire a sufficient positive voltage therein for overcoming the cathode bias is delayed until the capacitor 70 is fully charged and no longer drawing olf the R.F. current.

With this positive voltage on the grid 72, the plate current in the tube 74 will increase, thereby energizing the excitor coil 92 of the relay 94 so that the movable contact 96 will engages the fixed contact 98 and the movable contact 104 will be moved away from the fixed contact 106. Energization of the relay 94 will allow a continuing source of electric current to energize the valve 118 and fluid will flow out of the container 114. Upon this occurrence, the level of the material will fall thus changing the capacitance between the level thereof and the electrode 124 until the oscillation ceases in the circuit 10 and the positive voltage fed to the grid 72 terminates.

Normally this change in capacitance would be immediately felt at the grid 72 for decreasing the current in the anode circuit 76 for deenergizing the relay 94. However, since the capacitor 70 has been charged during the interval that the electrode 124 was in contact with the material A, when oscillation stops in the circuit 10 and the R.F. current is no longer induced on the grid 72, the capacitor 70 will discharge through the back resistance of the diode 66 and the resistor 79. This discharge of the current in the capacitor 70 will induce a positive voltage on the grid 72 and maintain energization of the relay 94 until the charge on the capacitor 70 has decreased sufiiciently so that the current limiting bias from the winding 88 and the cathode resistor 90 becomes effective once again, and the relay 94 will become deenergized due to the decreased current in the anode circuit of the tube 74.

The time delay for the discharge of the capacitor 70 results from the time required to discharge the same through the resistor 79 and this delay conveniently may be varied by varying the value of the resistor 79. It will be apparent that by increasing the resistance of the resistor 68, which is ordinarily used to limit the charge in the current through the diode 66, the time required to charge the capacitor 70 can be made to equal the time required to discharge the capacitor 70.

In the event of power failure, or failure of the tubes and 74, the relay 94 will become deenergized permitting the spring 100 to force the movable contact 96 away from the fixed contact 98 thus opening the circuit to the valve 118. Simultaneously with this actuation of the movable contact 96, the movable contact 104 will be moved into engagement with the fixed contact 106 for indicating a low level of the material A.

In the embodiment of Fig. 2, the electronic circuit and the component parts thereof are similar to that shown in Fig. 1 except that the capacitor 38 is grounded at 140, the R.F. choke 56 is removed from the plate circuit of the tube 20 and a pump 142 is connected by the conductors 120, 119 to the contact 106 and the line supply L2 respectively, for feeding the material into the container 114 when the relay 94 is energized. Also, capacitor 30 is connected in parallel with coil 28.

In operation, the capacitor 34 is adjusted until the oscillator circuit 10 oscillates with the level of the material A somewhat below the electrode 124. As in the embodiment of Fig. 1, when the circuit 10 oscillates, the capacitor 70 will be charged, the relay 94 will be energized to close the circuit to the pump 142 and fluid will flow into the container 114.

As the fluid level rises toward the electrode 124, the capacitance between the electrode 124 and the level of the material A will vary sufficiently to suppress oscillation in the circuit 10 thereby terminating the R.F. voltage generated in the coil 28. Consequently, the positive voltage fed to the grid 72 of the tube 74 from the oscillator circuit 10 becomes insufficient to efiect the limiting current in the cathode circuit of the tube 74. However, the tube 74 continues to pass current to the plate circuit sufliciently to delay the deenergization of the relay 94 until the capacitor 70 discharges the charge induced therein by the oscillator circuit 10. Therefore it will be apparent that the level of the material will continue to rise to a point above the level at which the material would normally occupy if no delay was encountered. Conversely, the level will recede to a point below the desired level before energization of the relay is made once again.

While the values of the circuit elements shown in the drawing are not critical, the values listed in the following table of values for the various elements have been most satisfactory in the operation of the present invention:

Resistance of the resistor 54 5000 ohms. Resistance of the resistor 68 680 ohms. Resistance of the resistor 180 ohms. Capacity of the capacitor 30 500 fd. Capacity of the capacitor 34 5-140 fd. Capacity of the capacitor 38 .01 fd. Capacity of the capacitor 70 8 fd. Capacity of the capacitor 82 fd. Inductance of the choke 56 2.5 millihenries. Output of the secondary 44 250 volts. Output of the secondary 88 6.3 volts.

The control apparatus of the embodiment of Fig. 2 operates as a capacity type high level fail-safe control switch since in the event of power failure or filament tube burn-out, the relay 94 will be deenergized or remain in its deenergized position. The level of the fluid A in the container 114 will appear to be at the level of the electrode 124 regardless of the actual level in the container, such appearance being indicated by the lamp 108. In any event, if the level of the fluid is at the electrode 124, or there is a failure in the circuit, the

operator of the controlled apparatus will be warned that the tank is either filled or that the system is inoperative without experiencing the danger of an overflowing container.

In the embodiment of Fig. 1, any power failure or tube burn-out will result in an indication that the container 114 is low without running the risk that the container is empty. It will be apparent to those skilled in the art that many modifications of the disclosed embodiments of the invention may be made without departing from the scope thereof, which is to be measured by the appended claims,

We claim:

1'. In amechanism for controlling the level of flowable material in a container, the combination comprising, an electronic oscillator circuit, a source of voltage connected to said, oscillator circuit, a probe operably connected to vary the impedance of said circuit for controlling oscillation therein in accordance with the level of flowable material, relay means operably connected to control the flow of flowable material and being movable between positions in response to changes in the flow of current therethrough, an electron discharge device operably connected to a source of voltage for controlling the flow of current through said relay means, said discharge device including an anode connected to said relay means and a grid for controlling the flow of current through said anode, a diode operably connected to said grid, time delay means comprising a capacitor and a resistor in parallel and being grounded at one end and connected at the other end to said diode and said grid, and coil means inductively coupling said oscillator circuit and said diode and being operable in response to initiation of oscillation to charge said capacitor and bias said grid to energize said relay means, said diode being operable in response to cessation of oscillation to delay de-energization of said relay means in such a manner that said capacitor biases said grid to maintain a flow of current throughsaid discharge device until said capacitor discharges a predetermined amount through said resistor, said relay means being operable to allow the material to fiow during this period of delay.

2. In a mechanism for controlling the level of flowable material in a container, the combination comprising an. electronic oscillator circuit, a source of voltage connected to said oscillator circuit, a probe connected tovary the impedance of said circuit 'toinitiate oscillation therein in accordance with the level of the flowable material for generating an alternating voltage in said circuit, a control circuit connected to a source of voltage and including a relay responsive to said alternating voltage for controlling the flow of material in accordance' with the energization of said relay, an electron discharge device connected to saidrelay and being oper-- able in response to current-flow therethrough to enerdelay means, said coil being inductively coupled with said oscillator circuit in such a manner that said rectifier charges said capacitor and biases said grid upon initiation of oscillation, and that said capacitor discharges through said resistor and delays de-energization of said relay upon cessation of oscillation to allow material to flow during such period of delay.

3. The device of claim 2 wherein said resistor is adjustable to vary the length of the delay of de-energization and vary the level at which the flow of material is cut off.

4. In a mechanism for controlling the level of Howable material in a container, the combination comprising an electronic oscillator connected to a source of voltage and including a tank coil, a capacitive probe connected to said oscillator and being operable in response I to the level of flowable material within the container for controlling oscillation in said oscillator, relay means operably connected to control the flow of material within the container, said relay means being movable between positions in response to changes in current flow therethrough, a control circuit operably connected to a source of voltage for controlling the flow of current through and the energization of said relay means, said control circuit'including an electron discharge device having at least an anode connected to said relay means, and a grid, said control circuit further including a coil inductively coupled with said tank coil of said oscillator, and time delay means operably connected between said coil and said grid for delaying the energization and de-energization of said relay in response to changes in oscillation within said oscillator, said time delay means comprising a. diode connected on one side to said coil and on'the other side to said grid, acapacitor and a variable resistor connected in parallel and being further connected at one end of said parallel connection to said other side of said diode and said grid, said capacitor and said variable resistor being connected at the other end thereof to the other end of said coil and being operable during the period of delay of de-energization to allow material to flow. f

References Cited in the file of this patent 0 UNITED STATES PATENTS Rockafellow Sept. 10, 

